Impeller change Mercury 40 OB

[mooregecko]

How do I remove the impeller from a Mid 70's Mercury 40 (4hp). I have already removed the lower unit and the top of the water pump. The old impeller was shredded. I removed all of the rubber from the old impeller down to what looks like a brass nut. Seems like the brass nut would slide up the drive shaft but it doesn't work that way. Do I have to remove the drive shaft? <br /><br />I can not buy a manual and was hoping somebody could go over this models impeller change procedures with me.

 

[Laddies]

Re: Impeller change Mercury 40 OB

You need to turn the imp. hub with the rotation of the shaft and that should release it so it can be pried up the shaft. You will need to grease the drive pin to hold it in place to replace the imp.

 

[Silvertip]

Re: Impeller change Mercury 40 OB

You don't need to buy a manual. Visit your local library. They generally have service manuals. May not be one exactly matching your motor but there will be one close.

 

[Silvertip]

Re: Impeller change Mercury 40 OB

If the impeller was shredded pieces may have become lodged in the power head so make sure you keep an eye on the tell tale and make sure the overheat horn is working.

 

[mooregecko]

Re: Impeller change Mercury 40 OB

I am sure that there is no overheat horn. I ended up just chiseling the bras "nut" off and the I was able to keep the pin after all said and done. I went to a neighbors house and borrowed his manual. He has a lot simpler impeller change process than I do. Anyways 6 hours to remove it and I am toast so I will let you know how it runs late tomorrow. As always I really appreciate the advice. It just keeps coming.

 

[mooregecko]

Re: Impeller change Mercury 40 OB

Still not pumping water after all said and done. The Marina told me this was the right impeller. Are they supposed to come to the edge fo the water pump houseing or be a little bigger and curl around? Also there was a left over part (as always). I failed to notice where it came from. It's a rubber washer about 1/4" thick. Any suggestions? I can get forced air through the pee hole but not a weed whaker string. Any ideas what other type of tools to use to clean any possible clogs from the impeller up? <br /><br />Again, Thanks

 

[GA Paramedic]

Re: Impeller change Mercury 40 OB

sounds like you have part of the old impeler stuck in the way. You may have to remove the line from your block to the pee hole and check it for blockages. Don't know about that exact model but on mine, looking at the back of the motor is a plate that goes around the spark plugs. remove that and you should find all sorts of parts to your impeller. Try to be careful removing it so you won't have to replace that gasket. if your blockage is any lower than that, you need someone with more experience than me because that is as far as I have ever had to go to unblock one.

 

[AMD Rules]

Re: Impeller change Mercury 40 OB

The 1/4" rubber part is a flinger that sits on the shaft just above the water pump housing.<br /><br />When running it, it may take a moment to get the water up to the outlet.<br /><br />Impellers are larger than the housing, and will curl up as you rotate the shaft during installation. I typically use dish soap if it is stubborn. <br /><br />Are you sure the impeller is turning with the shaft? Did you re-install the key properly?<br /><br />Are you certain that the water tube is inserted into the pump housing properly?<br /><br />On you're 4hp, I believe you have a plate on the rear part of the lower pan that routes the water out. You may find that parts of the old impeller are blocking those ports under that cover. That plate is mounted with small phillips screws if I recall. If its not there, you may need to remove the water jacket cover plate as 'boat medic' mentioned above. Be careful not to break the bolts if you do that. They may be corroded. Heat is your friend for stubborn bolts.<br /><br />Good luck.

 

[mooregecko]

Re: Impeller change Mercury 40 OB

Thanks guys, I found the plate that you were refering to and removed it with gasket intact. It was a bugga. There was no shrapnel in there so I dug deeper. All said and done, the new impeller, I found, has sucked a peice of the old impeller into it's path and I believe that's what was stopping it from working (so it came from below). However while I was "digging" I found some definate signs of wear on a lot of the gaskets so I will be looking for a gasket kit for a rebuid. Then I will test it out and let you know. Have any of you replaced lower end gaskets before? If so, can I get away with a marine forma gasket instead? Is there such a thing? <br /><br />Thanks again,<br />Dave